A SYSTEMATIC REVIEW ON THE EPIDEMIOLOGY OF CHOLERA
Cholera is an infection of the small intestine by some strains of the bacterium Vibrio cholerae. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting and muscle cramps may also occur. Diarrhea can be so severe that it leads within hours to severe dehydration and electrolyte imbalance. This may result in sunken eyes, cold skin, decreased skin elasticity, and wrinkling of the hands and feet. The dehydration may result in the skin turning bluish. Symptoms start two hours to five days after exposure.
Cholera is caused by a number of types of Vibrio cholerae, with some types producing more severe disease than others. It is spread mostly by water and food that has been contaminated with human feces containing the bacteria. Insufficiently cooked seafood is a common source. Humans are the only animal affected. Risk factors for the disease include poor sanitation, not enough clean drinking water, and poverty. There are concerns that rising sea levels will increase rates of disease. Cholera can be diagnosed by a stool test. A rapid dipstick test is available but is not as accurate
REVIEW ON THE EPIDEMIOLOGY OF CHOLERA
Cholera affects an estimated 3–5 million people worldwide and causes 58,000–130,000 deaths a year as of 2010. While it is currently classified as a pandemic, it is rare in the developed world. Children are mostly affected. Cholera occurs as both outbreaks and chronically in certain areas. Areas with an ongoing risk of disease include Africa and south-east Asia. While the risk of death among those affected is usually less than 5%, it may be as high as 50% among some groups who do not have access to treatment. Historical descriptions of cholera are found as early as the 5th century BC in Sanskrit. The study of cholera by John Snow between 1849 and 1854 led to significant advances in the field of epidemiology.
Cholera is an acute infection of the small intestine that is a particular problem in developing countries where access to clean drinking water and hygiene measures are poor. The disease causes severe diarrhea and vomiting leading to dehydration. Children and the elderly are at particular risk of rapidly developing and succumbing to the dehydration caused by cholera.
Over the last century, the number of cholera cases and deaths due to cholera have steadily declined, mainly due to improvements in sanitation and water hygiene. In England for example, no cases of cholera have originated in the country since 1893 and those that have been reported have been caught abroad.
Some of the regions where cholera is still a major health threat include:
• Sub-Saharan Africa or the countries south of the Sahara desert
• Some parts of the Middle East
• South and south-east Asia including India and Bangladesh
• Some parts of South America
In these regions, cholera is not a regular occurrence but may sometimes occur as outbreaks, especially during the summer season, natural disasters, wars or civil disorders. The outbreaks are almost always due to overcrowding of people living in poor conditions and with a lack of access to clean drinking water.
Cholera was first seen to spread as a pandemic to different parts of the world from the Indian subcontinent in 1817. The current pandemic originated in Sulawesi, Indonesia in 1961 and was caused by the El Tor biotype of the Vibrio cholerae serotype O1. It began to spread rapidly to other countries in Asia, Europe and Africa and even to Latin America in 1991.
Following this was the identification of a new strain called Vibrio cholerae O139 Bengal that caused outbreaks in India and Bangladesh in 1992. This strain is still confined to Asian countries.
Vibrio cholerae, the bacterium that causes cholera, is usually found in food or water contaminated by feces from a person with the infection. Common sources include:
• Municipal water supplies
• Ice made from municipal water
• Foods and drinks sold by street vendors
• Vegetables grown with water containing human wastes
• Raw or undercooked fish and seafood caught in waters polluted with sewage
When a person consumes the contaminated food or water, the bacteria release a toxin in the intestines that produces severe diarrhea.
It is not likely you will catch cholera just from casual contact with an infected person.
Cholera has been found in two animal populations: shellfish and plankton. Cholera is typically transmitted to humans by either contaminated food or water. Most cholera cases in developed countries are a result of transmission by food, while in the developing world it is more often water. Food transmission occurs when people harvest seafood such as oysters in waters infected with sewage, as Vibrio cholerae accumulates in zooplankton and the oysters eat the zooplankton.
People infected with cholera often have diarrhea, and disease transmission may occur if this highly liquid stool, colloquially referred to as “rice-water”, contaminates water used by others. The source of the contamination is typically other cholera sufferers when their untreated diarrheal discharge is allowed to get into waterways, groundwater or drinking water supplies. Drinking any infected water and eating any foods washed in the water, as well as shellfish living in the affected waterway, can cause a person to contract an infection. Cholera is rarely spread directly from person to person. Both toxic and nontoxic strains exist. Nontoxic strains can acquire toxicity through a temperate bacteriophage. Coastal cholera outbreaks typically follow zooplankton blooms, thus making cholera a zoonotic disease.
Symptoms of cholera can begin as soon as a few hours or as long as five days after infection. Often, symptoms are mild. But sometimes they are very serious. About one in 20 people infected have severe watery diarrhea accompanied by vomiting, which can quickly lead to dehydration. Although many infected people may have minimal or no symptoms, they can still contribute to spread of the infection.
Signs and symptoms of dehydration include:
• Rapid heart rate
• Loss of skin elasticity (the ability to return to original position quickly if pinched)
• Dry mucous membranes, including the inside of the mouth, throat, nose, and eyelids
• Low blood pressure
• Muscle cramps
If not treated, dehydration can lead to shock and death in a matter of hours.
A rapid dipstick test is available to determine the presence of V. cholerae. In those samples that test positive, further testing should be done to determine antibiotic resistance. In epidemic situations, a clinical diagnosis may be made by taking a patient history and doing a brief examination. Treatment is usually started without or before confirmation by laboratory analysis.
Stool and swab samples collected in the acute stage of the disease, before antibiotics have been administered, are the most useful specimens for laboratory diagnosis. If an epidemic of cholera is suspected, the most common causative agent is V. cholerae O1. If V. cholerae serogroup O1 is not isolated, the laboratory should test for V. cholerae O139. However, if neither of these organisms is isolated, it is necessary to send stool specimens to a reference laboratory.
Infection with V. cholerae O139 should be reported and handled in the same manner as that caused by V. cholerae O1. The associated diarrheal illness should be referred to as cholera and must be reported in the United States
The World Health Organization recommends focusing on prevention, preparedness, and response to combat the spread of cholera. They also stress the importance of an effective surveillance system. Governments can play a role in all of these areas, and in preventing cholera or indirectly facilitating its spread.
Although cholera may be life-threatening, prevention of the disease is normally straightforward if proper sanitation practices are followed. In developed countries, due to nearly universal advanced water treatment and sanitation practices, cholera is no longer a major health threat. The last major outbreak of cholera in the United States occurred in 1910–1911. Effective sanitation practices, if instituted and adhered to in time, are usually sufficient to stop an epidemic.
Prevention involves improved sanitation and access to clean water. Cholera vaccines that are given by mouth provide reasonable protection for about six months. They have the added benefit of protecting against another type of diarrhea caused by E. coli. The primary treatment is oral rehydration therapy—the replacement of fluids with slightly sweet and salty solutions. Rice-based solutions are preferred. Zinc supplementation is useful in children. In severe cases, intravenous fluids, such as Ringer’s lactate, may be required, and antibiotics may be beneficial. Testing to see what antibiotic the cholera is susceptible to can help guide the choice.
Cholera is an infectious disease that causes severe watery diarrhea, which can lead to dehydration and even death if untreated. It is caused by eating food or drinking water contaminated with a bacterium called Vibrio cholerae.
Cholera was prevalent in the U.S. in the 1800s, before modern water and sewage treatment systems eliminated its spread by contaminated water. Only about 10 cases of cholera are reported each year in the U.S. and half of these are acquired abroad. Rarely, contaminated seafood has caused cholera outbreaks in the U.S. However, cholera outbreaks are still a serious problem in other parts of the world. At least 150,000 cases are reported to the World Health Organization each year. The disease is most common in places with poor sanitation, crowding, war, and famine. Common locations include parts of Africa, south Asia, and Latin America. If you are traveling to one of those areas, knowing the following cholera facts can help protect you and your family.
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